Known in the art are carbamic acid derivatives of the general formula R(NHCOOR').sub.n, wherein R and R' are aromatic radicals, n is at least 2, which are useful in the application areas specified hereinabove (cf. J. H. Saunders, K. C. Frish Polyurethanes. Chemistry and Technology. Part I.Chemistry Interscience Publ., N.-Y.-London, 1962; U.S. Pat. No. 3,317,463 published 1967 Cl.260-47).
These compounds are prepared by reacting isocyanates with various substances containing reactive hydroxy groups, predominantly with phenol or substituted phenols.
When admixed to different diols or polyos, these compounds form compositions which are rather stable at normal temperatures. However, upon heating of such compositions destruction of carbamic acid derivatives occurs with liberation of isocyanates, wherefore they are referred to as blocked or masked isocyanates. The liberated isocyanates enter into reaction with diols or polyols of the composition to give a polyurethane polymer. The temperature at which an intensive decomposition of the carbamic acid derivatives occurs in contact with a hydroxyl compound is referred to as the exchange decomposition temperature. This temperature defines the curing temperature of compositions incorporating the above-specified compound.
The carbamic acid derivatives mentioned hereinbefore have a high exchange decomposition temperature (above 150.degree. C.). This substantially limits opportunities for their application, for example as adhesives for the materials possessing no high thermal stability.
Furthermore, curing of a composition in this case is accompanied by evolution, into the environments, of vapours of a very toxic phenol formed upon decomposition of the above-mentioned compounds.
Known in the art are modes for lowering the exchange decomposition temperature of carbamic acid derivatives comprising isocyanates blocked by phenols through the addition, thereto, of quaternary ammonium bases and organo-tin compounds (cf. U.S. Pat. Nos. 3,668,186; 3,676,402; published 1972). These processes make it possible to slightly lower the exchange decomposition temperature of the above-indicated compounds, but they fail to eliminate the difficulties associated with evolution of strongly toxic phenol vapours into the environments upon curing of the composition.